“However, the compiler arranges for it to work anyway.”

There are some things you don't want to hear from a language manual...

You might expect this not to work if it was compiled and res was not declared special, since non-special compiled variables are not represented as symbols. However, the compiler arranges for it to work anyway.

...especially not in the section on a low-level primitive like, say, pointers.

That's from page 110 of the 1979 Lisp Machine manual (20 MB of interesting history).

Unlike most lisps, Lisp Machine Lisp had pointers, called “locatives”: first-class places, implemented as (unboxed, IIUC!) pointers. One of their uses was to refer to variables by pointing to their names' value cells. But local variables generally don't live in their names' value cells, so locatives on them do nothing useful (and potentially something harmful). Apparently there was a workaround for this: the compiler recognized these locatives as intended to refer to local variables, and replaced them with something else.

Isn't it nice using a language with clean, well-specified semantics?